The present invention relates to controlled release unit dose formulations containing an antihyperglycemic drug. More specifically, the present invention relates to an oral dosage form comprising a biguanide such as metformin or buformin or a pharmaceutically acceptable salt thereof such as metformin hydrochloride or the metformin salts described in U.S. Pat. Nos. 3,957,853 and 4,080,472 which are incorporated herein by reference.
In the prior art, many techniques have been used to provide controlled and extended-release pharmaceutical dosage forms in order to maintain therapeutic serum levels of medicaments and to minimize the effects of missed doses of drugs caused by a lack of patient compliance.
In the prior art are extended release tablets which have an osmotically active drug core surrounded by a semipermeable membrane. These tablets function by allowing a fluid such as gastric or intestinal fluid to permeate the coating membrane and dissolve the active ingredient so it can be released through a passageway in the coating membrane or if the active ingredient is insoluble in the permeating fluid, pushed through the passageway by an expanding agent such as a hydrogel. Some representative examples of these osmotic tablet systems can be found in U.S. Pat. Nos. 3,845,770, 3,916,899, 4,034,758, 4,077,407 and 4,783,337. U.S. Pat. No. 3,952,741 teaches an osmotic device wherein the active agent is released from a core surrounded by a semipermeable membrane only after sufficient pressure has developed within the membrane to burst or rupture the membrane at a weak portion of the membrane.
The basic osmotic device described in the above cited patents have been refined over time in an effort to provide greater control of the release of the active ingredient. For example U.S. Pat. Nos. 4,777,049 and 4,851,229 describe an osmotic dosage form comprising a semipermeable wall surrounding a core. The core contains an active ingredient and a modulating agent wherein the modulating agent causes the active ingredient to be released through a passageway in the semipermeable membrane in a pulsed manner. Further refinements have included modifications to the semipermeable membrane surrounding the active core such as varying the proportions of the components that form the membrane; i.e., U.S. Pat. Nos. 5,178,867, 4,587,117 and 4,522,625 or increasing the number of coatings surrounding the active core; i.e., U.S. Pat. Nos. 5,650,170 and 4,892,739.
Although vast amounts of research has been performed on controlled or sustained release compositions and in particular on osmotic dosage forms, very little research has been performed in the area of controlled or sustained release compositions that employ antihyperglycemic drugs.
Metformin is an oral antihyperglycemic drug used in the management of non-insulin-dependent diabetes mellitus (NIDDM). It is not chemically or pharmacologically related to oral sulfonylureas. Metformin improves glucose tolerance in NIDDM patients by lowering both basal and postprandial plasma glucose. Metformin hydrochloride is currently marketed as GLUCOPHAGE® tablets by Bristol-Myers Squibb Co. Each GLUCOPHAGE® tablet contains 500, 850 or 1000 mg of metformin hydrochloride. There is no fixed dosage regimen for the management of hyperglycemia in diabetes mellitus with GLUCOPHAGE®. Dosage of GLUCOPHAGE® is individualized on the basis of both effectiveness and tolerance, while not exceeding the maximum recommended dose of 2550 mg per day.
Metformin has been widely prescribed for lowering blood glucose in patients with NIDDM. However, being a short acting drug, metformin requires twice-daily (b.i.d.) or three-times-a-day (t.i.d.) dosing. Adverse events associated with metformin use are often gastrointestinal in nature (e.g., anorexia, nausea, vomiting and occasionally diarrhea, etc.). These adverse events may be partially avoided by either reducing the initial and/or maintenance dose or using an extended-release dosage form. Another clear advantage of an extended release dosage form is a reduction in the frequency of administration. All of these findings suggest that an extended-release dosage form of metformin may improve the quality of therapy in patients with NIDDM and the safety profile relative to a conventional dosage form.
The limited work on controlled or sustained release formulations that employ antihyperglycemic drugs such as metformin hydrochloride includes the combination of the antihyperglycemic drug and an expanding or gelling agent to control the release of the drug from the dosage form. This research is exemplified by the teachings of WO 96/08243 and by the GLUCOPHAGE® metformin HCI product.
It is reported in the 50th Edition of the Physicians' Desk Reference, copyright 1996, p. 753, that food decreases the extent and slightly delays the absorption of metformin delivered by the GLUCOPHAGE® dosage form. This decrease is shown by approximately a 40% lower peak concentration, a 25% lower bioavailability and a 35-minute prolongation of time to peak plasma concentration following administration of a single GLUCOPHAGE® tablet containing 850 mg of metformin HCl with food compared to the similar tablet administered under fasting conditions.
A controlled release metformin dosage form is also described in WO 99/47128. This a reference describes a controlled release delivery system for metformin which includes an inner solid particulate phase formed of substantially uniform granules containing metformin and one or more hydrophilic polymers, one or more hydrophobic polymers and one or more hydrophobic materials, and an outer continuous phase in which the above granules are embedded and dispersed throughout. The outer continuous phase includes one or more hydrophilic polymers, one or more hydrophobic polymers and one or more hydrophobic materials.
Our own WO 99/47125 discloses controlled release metformin formulations providing a Tmax from 8 to 12 hours.